1. Field of the Invention:
This invention relates to control centers and more particularly to bus bars formed from sheet metal.
2. Description of the Prior Art:
In a motor control center the distribution of power by the bus bar system is a vital factor that influences the whole designed concept. More specifically, the vertical bus bar distributes power down a vertical stack of motor controllers arranged one on top of the other. Due to the variety of current ratings, such as 300, 600, and 800 amperes, vertical bus bars of various thicknesses and shapes have been adopted. For example, bus bars having cross sections that are Z, L, flat, cross, and circular, are provided to meet customer requirements.
Associated with the foregoing has been a problem of economics. Aluminum and copper, being excellent electrical conductors, are substantially interchangeable as material for bus bars. Aluminum, however, is less desirable, due to instant formation of non-conducting aluminum oxide on surface of raw aluminum exposed to the atmosphere. It can be used for plug-in connectors (stabs) only after special preparation of surface, to prevent the formation of oxides. Accordingly, copper is the preferred material for bus bars by most customers of motor control centers. The copper flat bar is much more expensive than aluminum flat bar or extrusion while copper extrusions are still costlier. Thus, copper extrusions of prior use are too costly to be economically competitive for use as vertical bus bars. As an alternative, copper shapes comprising roll-formed sheet metal are economically feasible as bus bars. Heretofore, a formidable disadvantage of roll-formed copper sheet metal as a substitute for copper extruded bus bars has been a difficulty of roll-forming copper sheet metal. The metallurgical properties of copper have not been conducive to roll forming of cold copper sheet metal to form a flange or leg of a bus bar having the desired thickness to which a clip-on connector of a circuit breaker is clipped on.